Igniter



G; LEWlN July 29, 1952 IGNITER Filed May 51, 1951 INVENTOR 652/907?) A EW/A/ 02% ATTORNEY Patented July 29, 1952 IGNITER I Gerhard Lewin, Maplewood', N.- J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 31, 1951, Serial No. 229,203

6 Claims. (Cl. 313-.355)

This invention relates to ignitors for ignitrons, and more particularly; to dielectric ignitors.

'A dielectric ignitor requires less firingenergy than a resistive ignitor, but despite this advantage, it has heretofore never successfully replaced the resistive ignitor commercially because it hasnot proven dependable enough for the purpose for which intended. The main difliculty has been that even the best dielectric ignitor ignitor heretofore attempted has exhibited a tendencyto puncture under the erosive action of the arc. I

An object of the invention is to provide an improved dielectric ignitor.

Morespecifically, an object of the invention is to provide a dielectric ignitor wherein, even though a puncture may occur, the puncture is harmless.

A further object of the invention is to take advantage of resistivity characteristics in event of puncture to temporarily maintain firing as a resistive ignitor during period of shorting due to the puncture and thereafter resume firing as a dielectric ignitor without interruption of firing.

Other objects of the invention will appear to those skilled in the art to which it appertains as the description proceeds, both by direct recitation and by implication from the context.

Referring to the accompanying drawing, in whichlike numerals of reference indicate similar parts throughout the several views:

Fig. 1 is a sectional elevationof an ignitron embodying the present invention in the ignitor shown therein;

Fig. 2 is a cross-section on line l"[II of Fig. 1;

Fig. 3 is a longitudinal section of a somewhat modified construction of ignitor; and

Fig. 4 is a cross-section on line IV-IV of Fig. 8.

In the accompanying drawing, arbitrary selection of one particular ignitron has been made within which to illustrate the ignitor of my conception, in its proper position of use, but the invention is not to be construed as restricted to the precise ignitron here depicted.

In the specific embodiment of the invention and associated ignitron construction illustrated in the drawing, especially Fig. 1 thereof, a cylindrical casing i is shown of steel or other sturdy material having a bottom l2 integral therewith and a top header l3 sealed at the upper rim of said casing to provide a closed enyelope adapted to be evacuated.

The header provides appropriate lead-in seals l4, l5 for electrode leads l6, I1 respectively for an anode l8 and ignitor [9 within the casing and supported from said header by said leads. The

lead-in seals each include a glass or'other insulating sleeve 20 by-which the leads are kept electrically distinct from each other and from the casing. The anode I8 is located toward the top of the casing, well above the bottom wall l2, whereas the ignitor I9 is located below the anode and is directed toward, and terminates at its bottom, inthe vicinity of said bottom wall and in contact with a cathode 2|. In the particular illustration, the cathode It comprises a pool of reconstructing liquid, such as mercury.

The present invention is directed more especially to ignitor construction. Two types of ignitors are known in the prior art, namely, a resistive ignitor and a dielectric'ignitor. It has been theorized that the resistive type functions byvirtue of resistance, the effect of which is that conduction current flowing through the ignitor into the pool cathode takes a very high density at the junction of the ignitor with the pool, and that the high current density with the associated high local electric gradient causes the arc to strike. The dielectricignitor functions by virtue of capacitance.- With dielectric ignitors, high field'is produced and displacement currents concentrate at the junction of the cathode with the ignitor, and an arc will strike thereat. According to the present invention, the ignitor functions both as a dielectric ignitor-and as a resistive ignitor, and in its general aspect comprises a thin conductive coating of resistive materiallocate'd within a thin-walled dielectric enclosure on the .inner surface of said wall or.

Walls.

According to the showing of Figs. 1 and 2, a sandwich of two juxtaposed strips or plates 22- of mica or other thin dielectric material with an interposed thin layer or coating 23 of resistive material, such as tantalum or graphite, constitutes the ignitor. The layer 23 is in electrical contact with the electrode lead II which preferably enters between the plates and terminates next the upper margin of the said layer or coating.

In the showing of Figs. 3 and 4, the dielectric enclosure is in the form of a thin-walled tube 22a of suitable dielectric material such as quartz, the bottom end of the tube being closed and having physical resemblance to a small test-tube. A layer or coating 23a of resistive material, such as tantalum or graphite, covers the inside surface of said tube and has electrical contact with the electrode lead I! which preferably enters the tube and terminates next the upper margin of the said layer or coating. 7

With either construction, or any other modified construction of enclosure. the wall thickness 3 of mica, glass or other dielectric, is preferably of the order of a few thousandths, say, one to five thousandths of an inch. Also, with either construction, the conductive coating is thin, and characterized by a minimum resistance of about one hundred ohms per square unit. Such a coating will have a firing characteristic similar to the dielectric ignitor and will readily erode.v

In constructions such as shown in Figs. 3 and 4 where a space exists internally of the enclosure, a suitable filler' 24 is included therein to exclude the mercury or other reconstructable liquid of the cathode from accumulation inside the enclosure either through the end of the enclosure or through any puncture which may occur. An arbitrarily selected filler 24 may comprise closely packed quartz powder, but the invention is not restricted to that material as there are others well known in the art which will perform the function satisfactorily.

Operation of the ignitor depends primarily upon the inherent capacitance existing between the pool cathode and the internal coating of the ignitor. In event of puncture of the enclosure wall, the pool material makes a short circuit through the puncture with said coating, whereupon the device continues to function as an ignitor by virtue of the resistive characteristic of the coating. The coating, however, is thin and under the intensity of the arc, is rapidly eroded in the region around the puncture, but the thinness of the space left within the enclosure due to the erosion deters entry of the cathode'material to maintain contact with the edge ofthe coating encircling the puncture and eroded region, whereupon the ignitor again functions as a dielectric or; capacitative ignitor. These shifts in operationfrom and to functioning asa resistive ignitor and as a dielectric ignitor occur automatically and without any interruption in the arc-striking functionof the ignitor and without any attention or manipulation by an attendant. Inasmuch as punctures occur infrequently, the life of the ignitor is not seriously impaired by the slight erosion of the coating around a puncture or around an accumulation of a plurality of punctures.

I claim:

l. Anignitor having a capacitative enclosure and having an internal resistive conductor the minimum resistance whereof is substantially one hundred ohms per square centimeter, whereby said ignitor has normal operation as a dielectric ignitor and is adapted to operate as a resistive ignitor in event of puncture of the enclosure.

2. An ignitor having a capacitative enclosure and having a thin coating of resistive material on the inner face of said enclosure, said coating having a minimum resistance of substantially one hundred ohms per square centimeter, whereby said ignitor has normal operation as a dielectric ignitor and is adapted to operate as a resistive ignitorin event of puncture of the enclosure.

3. An ignitor having a dielectric thin-wall enclosure and having an internal resistive conductor in contact with the wall of said enclosure, said resistive conductor having a minimum resistance of substantially one hundred ohms per square centimeter, whereby said ignitor has normal operation as a dielectric ignitor and is adapted to operate as a resistive ignitor in event of puncture of the enclosure.

4. An ignitor having a dielectric thin-Wall enclosure and having a thin coating of resistive material on the inner face of the wall of said enclosure, said coating having a minimum resistance of substantially one hundred ohms per square centimeter, whereby said ignitor has normal operation as a dielectric ignitor and is adapted to operate as a resistive ignitor in event of puncture of the enclosure.

5. An' ignitor having a capacitative enclosure and having an internal resistive conductor of tantalum the minimum resistance whereof is substantially one hundred ohms per square centimeter, whereby said ignitor has normal operation as a dielectric ignitor and is adapted to operate as a resistive ignitor in event of puncture of the enclosure.

v6. An ignitor having a capacitative enclosure and having an internal resistive conductor of graphite the minimum resistance whereof is substantially one hundred ohms per square centimeter, whereby said ignitor has normal operation as a dielectric ignitor and is adapted to operate as a resistive ignitor in event of puncture of the enclosure.

GERHARD LEWIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,365,608 Toep-fer Dec. 19, 1944 FOREIGN PATENTS Number Country Date 518,757 France Jan. 8, 1921 

